The 'Loving Kind' singer was believed to be holding crisis talks with the DJ after they split during a "huge bust-up" in September.
Sources claim that Crane has been providing continued moral support to Harding during her rehab stay for "depression and alcohol addiction", which has reignited the spark in their romance.
"Tom has flown out to be with her and help her through her problems," an insider told The Sun. "He felt partly responsible. They've been living a healthy lifestyle and rediscovering why they fell for each other in the first place. They both believe they can come out of this stronger than ever."
Another source said that although the reconciliation came with "sanctions" regarding their partying ways, both Harding and Crane "feel like they've been through too much together to let it go".
However, it is believed that the couple have put plans for their wedding on hold.
Harding and Crane became engaged on New Year's Day after dating for three years.
> Sarah Harding "doing really well" in rehab, says Kimberley Walsh